The present invention relates to a method of producing a thermoplastic sheet having a textured surface, the product produced by the method, and the method of using the thermoplastic sheet with textured surface to produce a composite layered product of dissimilar materials with interlocking interface between the layers, and the product produced thereby.
It has been known to create composite layered materials or products with dissimilar materials by using adhesive or chemical bonding between the dissimilar layers. The plastic materials have been notoriously difficult to successfully adhesively or chemically bond to one another. Many plastic materials after being adhesively or chemically bonded together are subject to difficulties associated with delamination, tensile-sheer, tensile-peel, impact resistance, wedge cleavage, and dynamic fatigue. In dynamic fatigue testing of adhesively bonded parts, the joint is loaded to a percentage of its typical breaking load and the cycles to failure are recorded. In addition to carrying out simulated load testing, evaluations are made in aggressive environments to estimate the service life of a part bonded with a particular adhesive. These tests can be carried out after conditioning the specimens at elevated temperatures, in humid aging, and after thermal cycling (thermal shock exposures). A mismatch in thermal coefficient of expansion of adhesive and substrates can lead to delamination or cracking in the adhesive layer. Even though many advances have been made in adhesive and chemical bonding techniques, the estimated service life of adhesively bond or chemically bonded plastic parts in particularly aggressive environments have been less than satisfactory.
It would be desirable to increase the service life of composite layered parts of dissimilar materials. Accordingly, a process is provided for manufacturing a part including the steps of molding a thermoplastic material into a generally planar sheet form having a textured surface on at least one side with a predetermined pressure between a die and a perforated insert, removing the molded thermoplastic material sheet and perforated insert from the die, and sintering the molded thermoplastic material sheet at a predetermined temperature for a predetermined period of time. The textured surface is defined by a plurality of projections or protuberances with at least one side wall extending outwardly from the sheet. The process can also include the step of stripping the sintered, molded, thermoplastic material sheet from the perforated insert, masking at least one side of the sintered, molded, thermoplastic material sheet for etching, and/or etching the textured surface of the sintered, molded, thermoplastic material sheet with a sodium-based etchant. The process according to the present invention can also include the steps of inserting the sintered, molded, thermoplastic material sheet into a molding die, introducing a dissimilar material into the molding die under pressure, and mechanically interlocking the thermoplastic material sheet to the dissimilar molded material with the plurality of protuberances. The mechanical interlocking of the thermoplastic sheet material to the dissimilar molded material is accomplished by deforming the plurality of protuberances during the molding step so that the at least one side wall of the protuberance moves into an angled orientation with respect to the thermoplastic material sheet to define a plurality of individual mechanical locking members along an interface between the thermoplastic material sheet and the dissimilar molded material. A portion of the molded dissimilar material is trapped between the angled side wall of each protuberance and the thermoplastic material sheet is mechanically interlocked along the interface with the dissimilar molded material.
A part manufactured according to the process of the present invention includes a thermoplastic material molded and sintered into a generally planar sheet form having a textured surface on at least one side. The textured surface is defined by a plurality of protuberances with at least one side wall extending outwardly from the sheet. The plurality of protuberances increases an effective surface area of the thermoplastic material sheet by at least 35%, or preferably by between 35% and 40%, inclusive. The protuberances can take any desired form, such as projections having cross sections that are circular, oval, triangular, rectangular, or other multi-sided configurations. Preferably, a circular cross section is provided. The part manufactured according to the process of the present invention can also include a dissimilar material layer molded to the textured surface of the sheet with a mechanically locked interface between the dissimilar material layer and the sheet as a result of deformation of the protuberances during the molding process to produce a composite layered product. The composite layered product can be used in a wide variety of applications, such as for valve diaphragms, pump diaphragms, bearing pads, or any application where delamination of dissimilar composite layered materials is a problem.
The thermoplastic material used in the process, or in the part, can be selected from the group consisting of fluoroplastic polymers, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) copolymers, perfluoroalkoxy (PFA) resins, polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene (ECTFE) copolymers, ethylene-tetrafluoroethylene (ETFE) copolymers, polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ultrahigh-molecular-weight polyethylene (UHMWPE), and mixtures thereof. Alternatively, the thermoplastic material used in the process according to the present invention, or in the part, can contain as a major constituent material selected from the group consisting of fluoroplastic polymers, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) copolymers, perfluoroalkoxy (PFA) resins, polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene (ECTFE) copolymers, ethylene-tetrafluoroethylene (ETFE) copolymers, polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ultra-high-molecular-weight polyethylene (UHMWPE), and mixtures thereof.
The dissimilar material used in the process according to the present invention, or in the part, can be selected from the group consisting of natural rubbers, vulcanized rubbers, butadiene-styrene copolymers, chloroprene polymers, nitrile rubbers, butadiene-acrylonitrile copolymers, isobutylene copolymers, butyl rubbers, polysulfide rubbers, ethylene-propylene rubbers, polyurethane elastomers, silicone rubbers, fluorocarbon elastomers, polyester elastomers, chlorinated rubbers, rubber hydrochloride, cyclized rubbers, chlorosulphonated polyethylene, and mixtures thereof. Alternatively, the dissimilar material used in the process according to the present invention, or in the part, can contain as a major constituent an elastomer material selected from the group consisting of natural rubbers, vulcanized rubbers, butadiene-styrene copolymers, chloroprene polymers, nitrile rubbers, butadiene-acrylonitrile copolymers, isobutylene copolymers, butyl rubbers, polysulfide rubbers, ethylene-propylene rubbers, polyurethane elastomers, silicone rubbers, fluorocarbon elastomers, polyester elastomers, chlorinated rubbers, rubber hydrochloride, cyclized rubbers, chlorosulphonated polyethylene, and mixtures thereof.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.